Delay Matching in Audio/Video Systems

ABSTRACT

An audio/video system comprises an audio signal processing path having an audio path delay and a video signal processing path having a video path delay. The audio path delay may be different from the video path delay. The audio path delay and/or the video path delay may change, for example because of replacement of a component within the audio signal processing path or the video signal processing path. Delay matching (synchronization) in the audio/video system comprises adjusting the audio path delay to be substantially equal to the video path delay. Matching the audio path delay to the video path delay generally includes adding delay to the signal processing path with the lesser delay.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims the priority benefit ofU.S. patent application Ser. No. 11/165,473 filed Jun. 22, 2005 andentitled “Delay Matching in Audio/Video Systems,” the disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention This invention relates generally toaudio/video systems and relates more particularly to delay matching inaudio/video systems.

2. Description of the Related Art

Many home theater systems today include a number of audio/video sourcesconnected to an audio/video processor and a video display. For example,the audio/video sources may include a DVD player, a satellite TVreceiver, a video game console and the like, for playing content such asa movie. The content from a selected audio/video source is decoded inthe audio/video processor to yield an audio portion and a video portion.The audio portion is decoded in the audio/video processor and playedthrough an audio amplifier and a number of audio speakers. The videoportion is shown on the video display, which may comprise an analogformat television (TV) or a digital format high-definition television(HDTV).

The audio portion and the video portion can be considered as beingprocessed through an audio signal processing path and a video signalprocessing path in the home theater system. One limitation with the hometheater system is that the audio signal processing path and the videosignal processing path can have differing delays. For example, the audiosignal processing path might have less than three frames of delay andthe video signal processing path might have six or more frames of delay(generally, an analog TV has a delay of about 1/60^(th) of a second inthe video signal processing path, in comparison with about ⅛^(th) to⅕^(th) of a second of delay for a digital HDTV). In general, a digitalTV has significantly more delay than an analog TV.

Differing delays between the audio signal processing path and the videosignal processing path can cause the audio portion of the content andthe video portion of the content to become “out of sync” in time (i.e.,the audio lagging behind the video, or with the video delayed withrespect to the audio). For example, in DVD video playback, an actor'slips may be moving out of sync with his speech, or a gunshot flash andits associated sound may not be coincident in time. As little as1/30^(th) of a second of time offset between the audio and videoportions can generally be detected by a viewer. In a specific example,the viewer can easily detect the actor's lips moving out of sync withhis speech if the audio portion leads the video portion by about 25milliseconds (msec) or more, or if the audio portion lags the videoportion by about 80 msec or more. The time mismatch between the audioportion and the video portion can cause significant distraction anddissatisfaction to the viewer.

SUMMARY

A system in accordance with the invention comprises an audio signalprocessing path configured to generate an audio stimulus, a video signalprocessing path configured to generate a video stimulus, a sensor, and adelay generator. The sensor is configured to detect a difference betweenan audio path delay of the audio signal processing path and a video pathdelay of the video signal processing path, based on the audio stimulusand the video stimulus. The delay generator is configured to adjust theaudio path delay to be substantially equal to the video path delay. Insome embodiments, the delay generator is configured to add delay intothe audio signal processing path if the audio path delay is less thanthe video path delay, and add delay into the video signal processingpath if the video path delay is less than the audio path delay.

In some embodiments, the audio signal processing path and the videosignal processing path comprise a home theater system, which maycomprise substitutable audio/video components. The sensor may comprisean audio/video camera, and may comprise a microphone and a light sensor.

A method comprises generating an audio stimulus in an audio signalprocessing path and a video stimulus in a video signal processing path,detecting the audio stimulus after an output of the audio signalprocessing path, detecting the video stimulus after an output of thevideo signal processing path, measuring a time offset between thedetected audio stimulus and the detected video stimulus, and determininga calibration value that substantially cancels the measured time offset.The method may include prompting a user to provide the audio stimulusand the video stimulus into an audio/video camera. The method mayinclude adding delay to the audio signal processing path if the detectedaudio stimulus leads (precedes) the detected video stimulus, or addingdelay to the video signal processing path if the detected video stimulusleads the detected audio stimulus.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a block diagram of an audio/video system (e.g. a hometheater) including a delay matching unit, in one embodiment inaccordance with the present invention;

FIG. 2 illustrates the delay matching unit of FIG. 1 including a manualslider for manual matching of the audio path delay and the video pathdelay, in one embodiment in accordance with the present invention;

FIG. 3 illustrates a method for fully automated delay matching in theaudio/video system of FIG. 1, in one embodiment in accordance with thepresent invention;

FIG. 4 illustrates a home theater room in which an audio/video systemincludes delay matching by incorporating a remote control withaudio/video sensors, in one embodiment in accordance with the presentinvention; and

FIG. 5 illustrates an optional calibration method for the audio/videosensor of FIG. 1, in one embodiment in accordance with the presentinvention.

DETAILED DESCRIPTION

Generally, an audio/video system comprises an audio signal processingpath having an audio path delay and a video signal processing pathhaving a video path delay. Delay refers to a time duration between aninput being presented to the audio/video system (e.g., by content suchas a movie played on a DVD player) and an output being generated by theaudio/video system (e.g., a frame of the movie displayed on a videodisplay). The audio path delay may be different from the video pathdelay. The audio path delay and/or the video path delay may change, forexample because of replacement of a component within the audio signalprocessing path or the video signal processing path. Delay matching(i.e., synchronization) in the audio/video system comprises adjustingthe audio path delay to be substantially equal to the video path delay.Matching the audio path delay to the video path delay generally includesadding delay to the signal processing path with the lesser delay.

As described further herein, methods for delay matching may be performedmanually or fully automatically. In manual matching, a user (viewer) ofthe audio/video system determines whether the audio path delay matchesthe video path delay, and accordingly adds delay to the appropriatesignal processing path to synchronize the audio path delay to the videopath delay. In fully automated calibration, the audio/video systemautonomously generates an audio/video stimulus, which stimulus isdetected by one or more audio and video sensors. The audio/video systemmeasures the time offset between the detected audio stimulus and thedetected video stimulus. The audio/video system adds delay to theappropriate signal processing path to synchronize the audio path delayto the video path delay.

Matching the delay between the audio signal processing path and thevideo signal processing path may be particularly beneficial inaudio/video systems such as home theater systems, in which audio/videocomponents with differing delays are connected or substituted over time.For example, replacing an analog TV with a digital HDTV may necessitatematching the delay between the audio signal processing path and thevideo signal processing path, because the digital HDTV may includesignificantly more video processing and video path delay than the analogTV. Similarly, replacing purely analog speakers with wireless speakersor speakers that include other audio processing circuitry such asdigital surround sound decoding may necessitate matching the delays inthe audio signal processing path with respect to the video signalprocessing path.

FIG. 1 illustrates a block diagram of an audio/video system (e.g., ahome theater) 100 including a delay matching unit 140, in one embodimentin accordance with the present invention. The audio/video system 100includes a number of audio/video sources for playing content: a Karaokeplayer 110, a DVD player 115, a satellite dish 120, a personal computer(PC) 125, and a video game console 130. Generally, one of theaudio/video sources 110-130, for example the video game console 130, isselected by a viewer for playing content. The audio portion of thecontent from the video game console 130 is decoded or otherwiseprocessed (e.g., amplified) by an audio processor 152 of an audio/videoprocessor 150. Similarly, the video portion of the content is decoded orotherwise processed by a video processor 151 of the audio/videoprocessor 150, for example by Moving Picture Experts Group (MPEG)decoding. Although depicted as separate component blocks, the audioprocessor 152 and the video processor 151 may be integrated into asingle physical component.

A video output 153 of the audio/video processor 150 drives a videodisplay 155. For example, the video output 153 may comprise compositevideo, S-video , or digital video such as High Definition MultimediaInterface (HDMI) or Digital Visual Interface (DVI) signals driving thevideo display 155. The video display 155 may comprise an analog TV, adigital HDTV, or other video monitor. The audio/video processor 150includes one or more audio outputs 154 to drive a number of audiospeakers 160. The audio speakers 160 may include left and right frontspeakers, left and right rear speakers, and a subwoofer, for example.

Although not specifically enumerated in FIG. 1, the audio/video system100 includes an audio signal processing path with an audio path delay.The audio signal processing path includes audio processing circuitrywithin the selected audio/video source 110-130, the audio/videoprocessor 150, and the audio speakers 160. The audio path delaycomprises the total delay in time between the content played by theaudio/video source 110-130 and the output of the audio speakers 160. Theaudio speakers 160 may contribute to the audio path delay, for exampleif the audio speakers 160 are connected to the audio/video processor 150by a wireless link, or other delay-inducing components such as digitalsurround sound decoding.

Similarly, the audio/video system 100 includes a video signal processingpath with a video path delay. The video signal processing path includesvideo processing circuitry within the selected audio/video source110-130, the audio/video processor 150, and the video display 155.Consequently, the video path delay comprises the total delay in timebetween the content played by the audio/video source 110-130 and theoutput of the video display 155.

As described further herein, the delay matching unit 140 is configuredto match the audio path delay with the video path delay by way of avideo delay generator 141 and/or an audio delay generator 142. The videodelay generator 141 and the audio delay generator 142 may compriseconfigurable analog delay lines or, preferably, digital delaymechanisms. For example, the video processor 151 and the audio processor152 of some embodiments include digital signal processing (DSP)circuitry (not shown). Based upon a determination that the video display155 is lagging (delayed in time from) the sound from the audio speakers160, the delay matching unit 140 may command the DSP circuitry to adddelay into the audio signal processing path by way of the audio delaygenerator 142. Alternatively, based upon a determination that the audiospeakers 160 are lagging (delayed in time from) the video display 155,the delay matching unit 140 may command the DSP circuitry to add delayby way of the video delay generator 141 into the video signal processingpath.

The delay matching unit 140 may be “upstream” (before) the audio/videoprocessor 150, or may be “downstream” (after) the audio/video processor150. Further, the delay matching unit 140 is shown as separate from theaudio/video processor 150 and the audio/video sources 110-130, but maybe integrated into the audio/video processor 150 or the audio/videosources 110-130. With the delay matching unit 140 integrated into theaudio/video sources 110-130, the audio and video portions of the contentfrom the audio/video sources 110-130 may be directly controlled by thedelay matching unit 140.

With the delay matching unit 140 as a separate unit from the audio/videosources 110-130, the assumption is made that the audio portion is insync the video portion from the audio/video sources 110-130, or thatmanual matching is performed as described with respect to FIG. 2.Further, as described with respect to FIGS. 3-4, the delay matching unit140 may be configured to generate an audio/video stimulus used to matchthe audio path delay and the video path delay in the system 100.

As described further with respect to FIGS. 3-5, the audio/video system100 includes an audio/video sensor 180. The audio/video sensor 180 isshown connected to the delay matching unit 140, but the audio/videosensor 180 may be connected to other devices within the system 100 suchas the Karaoke player 110 or the PC 125. The audio/video sensor 180provides hardware and/or software elements that allow the audio/videosystem 100 to detect and “timestamp” an audio/video stimulus, by whichthe audio/video system 100 may detect errors in synchronization of theaudio signal processing path and the video signal processing path. Forexample, the audio/video sensor 180 may comprise a microphone or otheraudio sensor capable of detecting an audio stimulus (e.g., a sound ortone) and determining a timestamp for the audio stimulus. Theaudio/video sensor 180 may include a light sensitive device such as aphotodiode or phototransistor, a charge-coupled device (CCD), or a CMOSimage sensor for detecting and determining a timestamp for a videostimulus. Typically, the audio/video sensor 180 has a predeterminedrelationship between the audio stimulus and its associated audiotimestamp, and the video stimulus and its associated video timestamp, ormay be calibrated within the system 100 as described further withrespect to FIG. 5.

The audio/video sensor 180 of some embodiments comprises an EyeToy™incorporating a CMOS image sensor, available from Sony ComputerEntertainment America Inc. of Foster City, Calif., connected to a SonyPlayStation®2 computer entertainment system, also available from Sony.In other embodiments, the audio/video sensor 180 comprises a “webcam”coupled to the PC 125, or a camcorder coupled to the Karaoke player 110.

The audio/video sensor 180 can be considered as able to detect theaudio/video stimulus “after” the outputs of the audio signal processingpath and the video signal processing path. For example, the audio/videosensor 180 detects the audio stimulus after it has been projected fromthe audio signal processing path into the environment (e.g., as anaudible sound) around the audio/video system 100. Similarly, theaudio/video sensor 180 detects the video stimulus after it has beenprojected from the video signal processing path (e.g., as a visiblelight pattern).

FIG. 2 illustrates the delay matching unit 140 of FIG. 1 including amanual slider 260 for manual matching of the audio path delay and thevideo path delay, in one embodiment in accordance with the presentinvention. The slider 260 is coupled to a video delay generator 251 andan audio delay generator 252 such that, based upon the position of theslider 260, additional delay is added into the audio signal processingpath or the video signal processing path.

The video delay generator 251 and the audio delay generator 252 maycomprise configurable analog delay lines or, preferably, digital delaymechanisms. For example, the video processor 151 and the audio processor152 of some embodiments include digital signal processing (DSP)circuitry (not shown). Based upon a determination by the viewer that thevideo display 155 is lagging (delayed in time from) the sound from theaudio speakers 160, the viewer may move the slider 260 and thencecommand the DSP circuitry to add delay into the audio signal processingpath by way of the audio delay generator 252. Alternatively, based upona determination by the viewer that the audio speakers 160 are lagging(delayed in time from) the video display 155, the viewer may move theslider 260 and thence command the DSP circuitry to add delay by way ofthe video delay generator 251 into the video signal processing path.

The slider 260 for controlling the delay of the audio signal processingpath with respect to the video signal processing path may be implementedin a number of ways. For example, in some embodiments, the slider 260comprises a “virtual slider” graphic element (not shown) displayed onthe video display 155 which the viewer can control by use of a frontpanel control or remote control. The slider 260 can be considered toadjust to the relative delay (i.e., relative time offset orsynchronization) between the audio signal processing path and the videosignal processing path in the audio/video system 100.

FIG. 3 illustrates a method for fully automated delay matching in theaudio/video system 100 of FIG. 1, in one embodiment in accordance withthe present invention. At step 310, the audio/video system 100 initiatesdelay matching of the audio signal processing path and the video signalprocessing path. In some embodiments, the audio/video system 100initiates matching in response to a request of the user. In alternativeembodiments, the audio/video system 100 initiates matching uponoccurrence of a predetermined event, such as upon power-up, upon theviewer changing the selected audio/video source 110-130, or at otherconvenient times, such as during a black pause before going to acommercial of a broadcast program.

In still other embodiments, the audio/video system 100 initiatesmatching based upon signals prestored on the media to be played by theaudio/video system 100 along with the desired content. For example,assuming audio and video outputs of the DVD player 115 are relativelywell synchronized, the signals that initiate matching of audio and videomay be stored on a DVD-ROM in the DVD player 115, along with the movie(content) to be played by the DVD player 115. The DVD-ROM may alsoinclude the actual audio and video stimuli by which the audio path delayand the video path delay are synchronized.

At step 320, the audio/video system 100 generates an audio stimulus byway of the audio speakers 160 and a video stimulus by way of the videodisplay 155. The audio stimulus and the video stimulus may besimultaneous, or may be offset by a predetermined time. The audiostimulus and the video stimulus may also comprise step-function,impulsive, or periodically changing signals. For example, the audiostimulus may cause a periodic change in the output of the audio speakers160 from inaudible to audible, or from one tone (frequency) to a secondtone, at about a 2 to 4 Hz rate. Similarly, the video stimulus may causethe video display 155 to change from a low intensity light output to ahigh intensity light output, to cycle between low and high intensitylight output at about a 2 to 4 Hz rate, and/or to change color, forexample from solid green to solid red.

In some embodiments, the audio stimulus comprises a predetermined audiotone of known duration with an associated video stimulus comprising asignal to switch the video display 155 from bright red to bright green.For example, the audio tone may be generated and persist forapproximately one-half second, during which time the video display 155displays bright red. Upon the end of the audio tone, the video stimulussubstantially simultaneously causes the video display 155 to switch tobright green. In other embodiments, the audio/video stimulus comprises avarying intensity of light output from the video display 155 byswitching between white and black screens, for example, in conjunctionwith an audio pattern such as two tones switching back-and-forth.

At step 330, the audio/video sensor 180 detects the change in the videodisplay 155 and the audio speakers 160 caused by the audio/videostimulus. Although the audio/video sensor 180 (e.g., the EyeToy) mayface the viewer and not directly face the video display 155, theaudio/video sensor 180 can detect light reflected off the face of theviewer or other objects in the room. Reflected light detection isgenerally sufficient in most viewing rooms in which the viewer prefersrelatively low ambient light levels. For example, the EyeToy cangenerally discern a bright green screen generated by the video display155 illuminating the room, because the color balance of the detectedimage is significantly changed with respect to a bright red screengenerated by the video display 155 illuminating the room. Alternatively,the audio/video sensor 180 may be pointed toward the video display 155to directly sample the light output of the video display 155, which maybe advantageous if the ambient light is very bright in the room, forexample because of direct sunlight.

Prior to step 330, the audio/video sensor 180 may have been programmedto provide filtering, time-gating, and/or threshold functions to preventfalse detection of the audio/video stimulus. For example, the EyeToy maybe programmed to disable auto white balance settings to enhance colorchange detection.

At step 340, the delay matching unit 140 measures the time offsetbetween the audio/video stimulus detected at step 330. At step 350, thedelay matching unit 140 computes a corresponding audio or videocalibration value to be applied to the audio signal processing path orthe video signal processing path that would substantially cancel themeasured time offset.

At step 360, the delay matching unit 140 applies the computed audio orvideo calibration value to the audio delay generator 142 or the videodelay generator 141. The calibration value substantially equalizes thedelays of the audio signal processing path and the video signalprocessing path.

An advantage of delay matching in the audio/video system 100 describedwith respect to FIGS. 1-3 is relatively easy, low cost delay matching.For example, the delay matching mechanisms described are easilyconfigured to operate with existing, commercially-available components.

FIG. 4 illustrates a home theater room in which an audio/video system400 includes delay matching by incorporating a remote control 410 withaudio/video sensors 415 and 420, in one embodiment in accordance withthe present invention. For simplicity of illustration and explanation,the audio/video system 400 depicted includes only a delay matching unit440, the audio/video processor 150, the video display 155, and audiospeakers 160, although other components such as the audio/video sources110-130 may be included in the audio/video system 400. In similarfashion to that described herein with respect to FIG. 1, the audio/videosystem 400 includes an audio signal processing path with an audio pathdelay and a video signal processing path with a video path delay (notnumbered).

The remote control 410 includes audio/video sensors: a microphone 415 todetect an audio stimulus, and a light sensor 420 to detect a videostimulus. The light sensor 420 of some embodiments comprises alight-sensitive photocell configured to detect whether the video display155 is lit or dark. In some embodiments, the light sensor 420 isconfigured to detect color changes in the video display 155.

The remote control 410 also includes timestamp and comparator circuitry425 to measure the time difference between the detected audio stimulusand the detected video stimulus. An infrared (IR) or radio frequency(RF, e.g. Bluetooth) transceiver 430 in the remote control 410 allowscommunication of the measured time offset to a corresponding transceiver450 in the delay matching unit 440. The remote control 410 may includefiltering, time-gating, and/or threshold circuitry to prevent falsedetection of the audio/video stimulus.

Referring to the method depicted in and described with respect to FIG.3, at step 310 the delay matching unit 440 of the audio/video system 400initiates delay matching of the audio signal processing path and thevideo signal processing path. At step 320, the audio/video system 400generates an audio stimulus and projects the audio stimulus into thehome theater room via the audio speakers 160. The audio/video system 400generates a video stimulus and projects the video stimulus into the hometheater room via the video display 155.

At step 330, the remote control 410 detects the audio/video stimulus.The microphone 415 detects the audio stimulus and the light sensor 420detects the video stimulus. The remote control 410 can be considered tobe detecting the audio/video stimulus after the outputs of the audiosignal processing path and the video signal processing path. Prior tostep 330, the remote control 410 may be initialized, for example to tunethe remote control 410 to detect the particular audio/video stimulus.

At step 340, the comparator circuitry 425 measures the time differencebetween the detected audio and video stimuli. The transceiver 430 of theremote control 410 communicates the measured time offset to thecorresponding transceiver 450 in the delay matching unit 440.

At step 350, the delay matching unit 440 computes a corresponding audioor video calibration value to be applied to the audio signal processingpath or the video signal processing path that would substantially cancelthe measured time offset. At step 360, the delay matching unit 440applies the computed audio or video calibration value to the audio delaygenerator 442 or the video delay generator 441. The calibration valuesubstantially equalizes the delays in the audio signal processing pathand the video signal processing path.

In an alternative embodiment, rather than the remote control 410measuring the time offset between the detected audio/video stimulus, theremote control 410 acts as a “mirror” with a predetermined delay withrespect to the incoming audio/video stimulus, and sends a mirror signalto be measured by the delay matching unit 440. The remote control 410has a deterministic delay between the time that it detects theaudio/video stimulus and the time that it transmits the mirror signal.For example, upon detecting the audio signal generated by the audiospeakers 160, the remote control 410 sends a first mirror signal to thedelay matching unit 440 after a predetermined delay, and upon detectingthe video signal generated by the video display 155, the remote control410 sends a second mirror signal to the delay matching unit 440 after apredetermined delay. Comparator circuitry (not shown) in the delaymatching unit 440 measures the time difference between the first mirrorsignal and the second mirror signal. The delay matching unit 440computes a corresponding audio or video calibration value to be appliedto the audio signal processing path or the video signal processing paththat would substantially cancel the measured time offset. The delaymatching unit 440 applies the computed audio or video calibration valueto the audio delay generator 442 or the video delay generator 441 tosubstantially equalize the delays in the audio signal processing pathand the video signal processing path.

The mirror signal may comprise an IR or RF signal to be detected by thecorresponding transceiver 450 in the delay matching unit 440.Alternatively, the mirror signal may comprise an IR or visual signal(e.g., from an LED on the remote control 410) to be detected by theaudio/video sensor 180 coupled to the delay matching unit 440. Forexample, a predetermined time after detecting the audio stimulus, theremote control 410 may transmit an IR signal to the delay matching unit440. A predetermined time after detecting the video stimulus, the remotecontrol may transmit a second IR signal to the delay matching unit 440.Comparator circuitry in the delay matching unit 440 measures the timebetween the first IR signal and the second IR signal, which time delaycorresponds to the difference between the audio path delay and the videopath delay. In this fashion, the remote control 410 acts like a mirrorwith a predetermined delay to signal detection of the audio stimulus andthe video stimulus so that the delay matching unit 440 can measure thetime offset between the audio and video stimuli.

An advantage of the embodiments described with respect to FIG. 4 is thatthe remote control 410 is typically in the “line of sight” of the videodisplay 155, and/or pointed at the video display 155, which obviates thedetection of reflected light as described with respect to FIG. 3.Another advantage is that the remote control 410 is in the reference ofthe viewer, not at the reference of the video display 155, so any flighttime delay in the room or reflections in the room are not included inthe computation of calibration values.

FIG. 5 illustrates an optional calibration method for the audio/videosensor 180 of FIG. 1, in one embodiment in accordance with the presentinvention. The method of FIG. 5 may be advantageous, for example, if theaudio/video sensor 180 is not known to accurately measure the relativetiming of audio and video stimuli detected in the audio/video sensor180.

The method provides an event in the real world (e.g., a handclap of theuser) to be sensed by the audio/video sensor 180, so that anyaudio/video sensor 180 (e.g., a camcorder or webcam) may be calibratedfor use in delay matching as described herein. For example, with awebcam for the audio/video sensor 180, the webcam may ‘see’ and ‘hear’the handclap and convert the handclap into an audio signal and a videosignal. The audio signal and the video signal into the PC 125 mayinclude unknown delays in the video and/or audio paths before thesignals reach the PC 125. If the audio/video system 100 measures thetime at which the PC 125 receives the audio and video signals resultingfrom the handclap, the PC 125 may receive the audio and video signals atdifferent times (out of synchronization). Essentially, the method ofFIG. 5 corrects mismatch of the audio path delay and the video pathdelay due to the audio/video sensor 180. In other words, a predeterminedsimultaneous audio and video event is used to calibrate the audio/videosensor 180 so that the audio stimulus and the video stimulus aremeasured as simultaneous even if the audio/video sensor 180 reportsotherwise.

At step 510, the user of the audio/video system 100 initiatesaudio/video sensor 180 calibration, for example by selecting a menuoption on a display (not shown) of the delay matching unit 140 or thevideo display 155. At step 520, the audio/video system 100 prompts theviewer to generate an audio/video stimulus. For example, the audio/videosystem 100 may prompt the viewer to stand relatively close to theaudio/video sensor 180 and say “Hi” into the audio/video sensor 180.Alternatively, the audio/video system 100 displays on the video display155 a live image of the viewer as captured by the audio/video camera(e.g., the EyeToy) 180, and superimposes a graphic of a box on the videodisplay 155 beside the image of the viewer. The audio/video system 100then prompts the viewer (e.g., by text on the video display 155) to claphis hands inside the box graphic.

At step 530, the audio/video sensor 180 detects the audio/videostimulus, e.g., the movement of the user's lips and the correspondingspeech, or the hands of the viewer entering the box on the video display155 and the sound of the associated handclap. The audio/video sensor 180then generates an audio timestamp and a video timestamp for the detectedaudio/video stimulus. The audio and video timestamps may be generated ina number of ways. For example, the detection of the audio stimulus maytrigger sampling of a running digital counter, which yields a digitaltimestamp for the audio signal.

At step 540, the delay matching unit 140 measures the time offsetbetween the detected audio stimulus and the detected video stimulus. Thetime offset may be computed by subtracting the lesser of the audiotimestamp and the video timestamp from the greater of the audiotimestamp and the video timestamp. At step 550, the delay matching unit140 computes a corresponding audio or video calibration value that wouldsubstantially cancel the measured time offset and synchronize the audiosignal processing path with the video signal processing path. Forexample, the calibration value may comprise a value that sets the audiopath delay equal to the video path delay, with a resolution less than1/30^(th) of a second. At step 560, the delay matching unit 140 appliesthe computed audio or video calibration value to substantially equalizethe detected delays in the audio signal processing path and the videosignal processing path from the audio/video sensor 180.

The invention has been described above with reference to specificembodiments. It will, however, be evident that various modifications andchanges may be made thereto without departing from the broader spiritand scope of the invention as set forth in the appended claims. Forexample, the audio/video sensors may be implemented in a variety ofways, the computation of the calibration value may be performed withvarious methods, and the sensing, measuring, and computation functionsmay be implemented in other parts of the audio/video system withoutdeparting from the scope of the invention. In a specific example, theaudio/video sensor 180 of FIG. 1 may be connected to the video gameconsole 130 which is directly connected to an HDTV video display 155with relatively large video path delay and to the audio speakers 160 viaan audio amplifier with little audio path delay. The functions of thedelay matching unit 140 and the audio/video processor 150 are thereforedistributed between the HDTV and the audio amplifier, but principles ofthe invention still apply for delay matching. In another example, amicrophone connected to the Karaoke player 110 may be used for detectingthe audio stimulus described with respect to FIG. 4. The foregoingdescription and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. A system for synchronizing audio signals and video signals, thesystem comprising: an audio signal processing path configured togenerate an audio stimulus; a video signal processing path configured togenerate a video stimulus; a sensor configured to detect a differencebetween an audio path delay of the audio signal processing path based onthe audio stimulus and a video path delay of the video signal processingpath based on the video stimulus, wherein the sensor comprises anaudio-video camera; and a delay generator configured to adjust the audiopath delay to be substantially equal to the video path delay.
 2. Thesystem of claim 1, wherein the delay generator is configured to adddelay into the video signal processing path if the audio path delay isgreater than the video path delay, or add delay into the audio signalprocessing path if the video path delay is greater than the audio pathdelay.
 3. The system of claim 1, wherein the audio signal processingpath and the video signal processing path comprise a home theatersystem.
 4. The system of claim 3, wherein the home theater systemcomprises substitutable audio/video components.
 5. The system of claim1, wherein the audio signal processing path and the video signalprocessing path include an audio-video processor, the delay generatorincluded within the audio-video processor.
 6. The system of claim 1,wherein the audio signal processing path and the video signal processingpath include an audio-video processor, and wherein the delay generatoris coupled to the audio-video processor.
 7. The system of claim 1,wherein the delay generator is further configured to adjust the audiopath delay equal to the video path delay with a resolution of less thanabout 1/30^(th) of a second.
 8. The system of claim 1, wherein the audiosignal processing path includes a player of media content, the mediacontent including the audio stimulus and the video stimulus.
 9. Thesystem of claim 8, wherein the player of media content comprises a videogame system.
 10. The system of claim 8, wherein the player of mediacontent comprises the delay generator.
 11. A method for synchronizingaudio signals and video signals, the method comprising: generating anaudio stimulus in an audio signal processing path and a video stimulusin a video signal processing path; detecting the audio stimulus after anoutput of the audio signal processing path, wherein detecting the audiostimulus comprises sensing the audio stimulus with an audio-videocamera; detecting the video stimulus after an output of the video signalprocessing path, wherein detecting the video stimulus comprises sensingthe video stimulus with the audio-video camera; measuring a time offsetbetween the detected audio stimulus and the detected video stimulus; anddetermining a calibration value that substantially cancels the measuredtime offset.
 12. The method of claim 11, further comprising: calibratingthe audio-video camera for detecting the audio stimulus by prompting auser to provide the audio stimulus to the audio-video camera; andcalibrating the audio-video camera for detecting the video stimulus byprompting the user to provide the video stimulus to the audio-videocamera.
 13. The method of claim 11, further comprising adding delaybased on the calibration value to the audio path if the detected audiostimulus precedes the detected video stimulus.
 14. The method of claim11, further comprising adding delay based on the calibration value tothe video path if the detected video stimulus precedes the detectedaudio stimulus.
 15. The method of claim 11, further comprisingcorrecting for measurement delays in a sensor configured to measure thetime offset.